Smoke Domain renders as a grayish box
Sorry this is not an answer. 

I will delete, just so I can post a pic. 

I just opened your file, disconnected all the image textures (because they were not packed) 

Then I just hit Render with all your settings and it doesnt have that same error that yours does. 

This is what I got. 



Maybe someone else can try your file and see if they can replicate it. It seems like a hardware glitch. Change to a GPU (if you can) see if that changes anything.